Magnets

[dustypuss]

Bar magnet

How long does the magnetism last in a bar magnet before it stops being a magnet !

[Old_Geezer]

When I Googled it was suggested they weaken at about 1% per decade.
I've no reason to doubt it, but ..... can't confirm either.

[gen2]

Rough handling, poor storage and exposure to high temperatures will all increase the rate at which the magnetism is lost.

[jomifl]

You need to re-phrase your question, with a normal log. decay curve it will retain some magnetism virtually forever in practical terms. However if you ask 'how long will it take to lose 50% of its magnetism' (ie it's half life) then someone might be able to answer your question. It would depend on many factors as previously mentioned.

[beso]

A magnet maintains its magnetisation better when the magnetic circuit is comleted. Store two bar magnets end to end or place a piece of steel along it to complete the circuit.

[sparkymick]

a magnet has a half life of 120 years - ie in 120 years it will have half its magnetism left.

[Graham-W]

As SparkyMick has said but to continue, after 240 years it would have 25% of its power left and after 360 years 12.5% and so on.

[dustypuss]

Thanks to all